For as many years as I have been playing, there are ALWAYS a few things that remain constant...

Be on time for the gig. Truth be told, "on time" is actually probably 30 mins before everyone is called for load in. I have found that it helps to be early. Time to meet the club owner and visit with the sound guy/gal. It never hurts to get a clue of the what and how things are like in that place(especially if it is the first time you play there.)

Show up with all the gear you need. Sometimes tools are required, maybe extra batteries if you play active basses, extra strings don't hurt...make sure your cables and adapters et al are ready to use.

(I know this goes without saying but...) BE PROFESSIONAL! It is not all about you all the time. Saying things to demean others or their opinions on various topics will not win you any new friends or fans. Whether a paying gig or not, you are there to provide a service and ensure that the crowd is being entertained. Own your part of that performance and if given instruction, take it without thinking that someone is being a control freak or worse.

If you are used to playing clubs/bars and smaller venues, your reaction to a sudden change(to LARGE venue) will be very important. Standing in front of a festival or arena sized audience can be freaky at first if you do not know what to expect. Bigger crowd means more energy so it is up to you, the professional, to know what to do with that energy and not let it distract or take away from your performance. (For a fun example, go back and watch the first episode of the Partridge Family to see reactions to first timer-itis...)

Unless you are required to 'vacate the premises' at the completion of your set, a healthy round of handshakes and chats is in order. Be approachable! There are people who have just seen the show and want to talk with you-even if just to say hi. Take time with people, they support you! There are stories of performers staying 2 hours or more after the show to talk with everyone/anyone who wants to visit, take pics, get autographs etc...again, be personable, these are your friends and fans who want to hear what you do. They are the ones who tell their friends about your show, they are the ones who BRING their friends for your next show.

There are a lot more topics to cover here....Bottom line, do what you do and have fun! After all, we are PLAYING music! Use your eyes and ears to make memories for others while you are at it. It is all about the experience for most people, give them a great time ans lots of memories!